Guanine Gua

The bases that occur in nucleic acids are aromatic heterocyclic compounds derived from either pyrimidine or purine. Five of these bases are the main components of nucleic acids in all living creatures. The purine bases adenine (abbreviation Ade, not A ) and guanine (Gua) and the pyrimidine base cytosine (Cyt) are present in both RNA and DNA. In contrast, uracil (Ura) is only found in RNA. In DNA, uracil is replaced by thymine (Thy), the 5-methyl derivative of uracil. 5-methylcyto-sine also occurs in small amounts in the DNA of the higher animals. A large number of other modified bases occur in tRNA (see p. 82) and in other types of RNA. 

Purine (left). The purine nucleotide guano-sine monophosphate (CMP, 1) is degraded in two steps—first to the guanosine and then to guanine (Gua). Guanine is converted by deamination into another purine base, xanthine. 

For higher DETA/NO concentrations, the DP voltammogram showed two large oxidation peaks for dGuo and dAdo plus a third peak at a lower potential, Epa — + 0.77 V (Fig. 20.10). This peak is a consequence of the interaction between peroxynitrite radicals and DNA, corresponding to guanine (Gua) oxidation. 

Fig. 1. Chemical structures of the DNA backbone (2-deoxyribose phosphate unit) and of the nucleobases thymine (Thy), cytosine (Cyt), guanine (Gua), and adenine (Ade).

B = adenine (Ade), cytosine (Cyt), guanine (Gua), thymine (Thy), uracil (Ura), or other natural or unnatural nucleobase p = nucleobase protecting group, e.g. benzoyl for Ade and Cyt or isobutyryl for Gua, Thy and Ura are normally left unprotected R = 5 -protecting group, e.g. 4,4 -dimethoxytrityl (DMTr)... 

From the species names, one may recognize some of the various participants in purine metabolism. The important purines guanine (Gua) and adenine (Ade) are both synthesized from inosine monophosphate (IMP). They may then be derived to (d)GTP and (d)ATP, respectively, prior to incorporation into nucleic acids like DNA and RNA. This simple explanation betrays the true complexity of purine metabolism, and elucidating the properties of such complex systems depends on sophisticated computational tools, which we describe presently. 

Transport Direction of Uracil (Ura), Cytosine (Cyt), Adenine (Ade), Guanine (Gua), and K+ Ion in the Transport against the Concentration Gradient of Them through the q-Chito Membrane... 

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